A few weeks ago, a reader asked about the origin of the wreath. She had heard that it was meant to be a symbol of Christ's crown of thorns. That connection is a stretch, but the wreath and other Christmastime foliage have symbolized many things over the centuries, some of them Christian.
The wreath seems to represent a convergence of two lines of tradition. One one side, it's probably related to circlets worn on the head. In cultures of the ancient Persian Empire, nobles wore diadems of fabric and sometimes jewels, and Greeks rewarded Olympic victors and other high achievers with laurel crowns. It's unclear how such headgear was transformed into wall decor, but perhaps people just hung their crowns up as souvenirs. Neither Christmas nor Advent wreaths are worn as headbands, though for the Swedish festival of St. Lucia, on December 13, the family's eldest daughter wears a headpiece decorated with greenery and nine lighted candles.
Though early Roman Christians used laurel in their Christmas decorations because it symbolized victory, glory, and cleansing from guilt, Europeans largely favored evergreens. This shows the modern wreath's other heritage: German and Celtic solstice festivities. In cold, northern climates, people latched onto anything that represented light and life against darkness and despair. As a result, their favorite winter symbols included torches (analagous to Advent candles) and plants that stayed green all year. A wreath with burning candles, then, is related to the Yule log—a good-luck charm held over from the 12-day Norse winter festival of Jol. Christmas candles may also be related to Hanukkah candles, as both of the nearly concurrent observances celebrate holy light.